Gastrointestinal monitoring systems measure one or more physiological properties at a location within the gastrointestinal (GI) tract of a subject. Systems that monitor reflux of gastric contents into the esophagus (gastroesophageal reflux) and also above the esophagus into the pharynx and larynx aid in diagnosis and treatment of various GI disorders and conditions, such as gastrointestinal reflux disease (GERD), heartburn, esophageal scarring (possibly accompanied by dysphagia), reflux esophagitis, Barrett's esophagus, laryngitis and chest pain. In physiological monitoring systems, values of physiological properties of interest (e.g. pH, pressure, temperature, etc.) are measured at a location within a body lumen or an organ of the subject, and information regarding the measured values is sent to a device external to the subject that receives the information and may record, analyze and/or transfer the information.
Some known upper GI (i.e. pharyngeal, esophageal, and gastric) pH measurement systems employ large diameter (typically ≧1.5 mm diameter) relatively stiff catheters that facilitate patient intubation. In such a system, a large diameter catheter is positioned with a detecting portion of the catheter within the patient and a proximal portion of the catheter exiting out through the patient's nose and extending to a remote data logging device, which is normally located at the patient's waist. The catheter remains within the patient throughout the monitoring process (typically about 24 hours), often causing pain and discomfort that may affect the patient's diet and ability to sleep and thereby negatively affect the degree to which collected data are representative of the true patient condition. Additionally, the patent may be self-conscious about the appearance of the catheter exiting the patient's nose and extending down the patient's neck, causing the patient to restrict his or her activities, such as work or other physical activities during monitoring.
Capsules that use micro-electronics and sensors have been developed for physiological measurements within the GI track (e.g. Smart Pill Diagnostics, Inc.). Such a remote sensing capsule wirelessly transmits physiological data (e.g. pH, temperature, pressure, etc.) measured at the capsule's current location as the capsule moves through the GI system. A known monitoring system including such a capsule may avoid the pain, discomfort and appearance issues associated with known catheter systems. However, the remote sensing capsules, which are swallowed, do not take measurements at a fixed location in the GI system over an extended period of time because a remote sensing capsule does not maintain a fixed location within the GI system and is carried along the GI tractover time.
One known method to fix an internal body location of a remote sensing capsule for measurements of esophageal pH is to tether the capsule to the patient's tooth. However, the tooth attachment method suffers from substantial drawbacks associated with operator difficulty with attachment of the tether to the tooth, and patient intolerance due to discomfort of the tether in the pallet including elicitation of the gag reflex.
Another method to fix an internal body location of a remote sensing capsule is implantation of an implantable remote sensing capsule within the GI tract of a subject (e.g. Bravo™, Medtronic, Minneapolis, Minn.). The remote sensing capsule may be implanted by a doctor using an endoscopic procedure requiring sedation or general anesthesia. Endoscopic implantation has a 2-4% risk of complications requiring emergency removal of the capsule. Another known implantation technique involves passing the capsule through the nasal passage; however, the large size of known remote sensing capsules, which include transmitters and batteries, may result in trauma to the patient during insertion of the capsule through the nasal passage.